Method and device for determinig available electric power in an instrument panel

ABSTRACT

The present invention relates to a method and a device for ascertaining the electric power, provided by a battery ( 11 ) and a generator ( 10 ), available in a motor-vehicle electrical system. To precisely determine the available electric power, both a battery model ( 2 ) and a generator model ( 4 ) are provided, from which the battery reserve power (ΔP battery ) and the generator reserve power (ΔP generator ) may be ascertained. The total power available in the vehicle electrical system is finally determined from the battery reserve power and the generator reserve power.

TECHNOLOGICAL FIELD

[0001] The present invention relates to a method and a device for ascertaining the power, provided by a battery and a generator, available in an energy supply system, particularly a vehicle electrical system.

[0002] The power requirement of electrical loads in motor vehicles is rising sharply due to the increasing number of comfort and convenience loads and the electrification of auxiliary systems. In certain operating states, the electric power made available by the generator is no longer sufficient to cover the entire power requirement. To be able to initiate selective measures within the framework of an electrical energy and load management, information is required concerning the instantaneous relationship of power supply and demand.

[0003] When using safety-critical electrical loads, such as electromechanical brakes (EMB), in a motor-vehicle electrical system, the energy supply of this system must be monitored constantly in order to be able to recognize a malfunction in a timely manner and initiate countermeasures. For this purpose, modern vehicle electrical systems include an energy and electrical load management system, by which it is possible to check the vehicle battery regarding its state of health prior to switching on a load. If there is danger of exceeding certain load limits of the battery, either measures may be carried out for improving the state of health of the battery, for example, by increasing the charging voltage, or measures may be carried out for reducing the battery load, particularly the switching-off or dimming of electrical loads.

[0004] A motor-vehicle electrical system is usually supplied by a battery and, when the engine is running, by a generator. The load capacity or state of health of a vehicle battery may be assessed using suitable battery models, making it possible to ascertain whether certain electrical loads may be switched on, or whether load-reducing measures must be initiated to prevent a failure of safety-critical devices. Such a battery model is described, for example, in DE-P 101 065 08.6. However, in that case, the power made available by the generator is not taken into account.

[0005] It may be that the degree of generator utilization may be ascertained via a so-called DF-signal (control signal by which the excitation of the generator is activated or deactivated). However, in this context, a conclusion about the instantaneous power output, and, above all, the instantaneous power reserve of the generator is not possible, since the power output of the generator is strongly dependent on the specific operating state (temperature, voltage, rotational speed, capacity utilization).

[0006] Therefore, the object of the present invention is to provide a method and a configuration which make it possible to more precisely determine the power available from the generator, in order to use this information for an optimum energy and electrical load management.

[0007] This objective is achieved by the features specified in Claims 1 and 15, respectively. Further refinements of the invention are the subject matter of the dependent claims.

[0008] The essential idea of the present invention is to ascertain the electric power, provided by a battery and a generator, available in a motor-vehicle electrical system, not only by evaluating a battery model, but in addition to set up a generator model with which the reserve power available from the generator may be exactly calculated. The reserve powers ascertained from the battery model and the generator model are finally balanced in order to calculate the reserve power available, or a power deficit, in the vehicle electrical system.

[0009] The generator model may be implemented both as software and as hardware (circuit). According to one preferred specific embodiment of the present invention, the generator model is supplied with the generator voltage, the generator speed and the generator temperature or variables from which the previously indicated parameters may be derived (such as the coolant temperature from which it is possible to estimate the generator temperature). By using the generator model, it is possible to ascertain the instantaneously available electric power and the power reserve of the generator as a function of the operating state (voltage, speed, temperature, capacity utilization) of the generator.

[0010] The generator model is preferably a program in which generator characteristic curves are stored which represent the profile of the generator voltage or output power as a function of specific operating parameters.

[0011] The information about the reserve power available in the vehicle electrical system, obtained from the power balancing, is used for an electrical load management. For example, load limits of the battery and/or generator may be predefined which are not to be exceeded when switching on an electrical load.

[0012] The reaction (voltage drop, increase in capacity utilization) of the battery or of the generator to be expected when switching on a defined electrical load may be predicted, for instance, using a suitable model. To that end, for example, the model compares a predefined maximum degree of utilization to the degree of utilization to be expected after switching on an electrical load. Such a comparison permits a clear statement about whether or not the battery or the generator is able to provide a minimum voltage required for the reliable operation of the electrical load in question.

[0013] The load of the battery or of the generator may be limited by steps, that is to say, different load limits may be predefined which are valid for different electrical loads. For example, provision may be made in the electrical load management (control unit with management program) that, above a predefined loading of the vehicle electrical system, only certain electrical loads may be switched on, but others not.

[0014] If the predefined load limits are exceeded, countermeasures are preferably initiated. Upon recognition of a power deficit, stabilization measures such as increasing the idling speed of the engine may be carried out, or the switch-off or dimming of electrical loads may be initiated.

[0015] According to one preferred embodiment of the invention, the exceeding of the predefined limiting values is displayed.

[0016] Given sufficient power reserve in the vehicle electrical system, the power surplus may be used for a battery thermomanagement, that is, the battery may be heated, thereby exhibiting better charging performance.

[0017] According to one preferred specific embodiment of the invention, the battery model may be supplied with battery measured values, particularly the battery voltage or the current delivered by the battery, in light of which the model parameters taken as a basis in the battery model may be adapted in the event of deviations. In this way, the battery model dynamically follows the instantaneous state of the battery which, as is known, steadily deteriorates during its service life.

[0018] In similar fashion, generator measured values, particularly the generator voltage, the generator speed and/or the generator temperature may also be supplied to the generator model used. However, in contrast to the battery model, the generator model is preferably static. The characteristic curves underlying the generator model, which were ascertained by test stand measurements as a function of temperature, load, etc., are preferably not changed.

[0019] According to one best mode of the invention, the generator voltage is estimated up to a predefined degree of utilization of the generator. Only as of a predefined degree of utilization of, for example, 90% (which may be obtained via the DF signal) is the generator voltage calculated from the battery voltage and a voltage dropping on the connection line to the battery.

BRIEF DESCRIPTION OF THE DRAWING

[0020] In the following, the invention is explained more precisely by way of example, with reference to the attached Drawing, in which:

[0021]FIG. 1 shows a schematic block diagram of a system for ascertaining the total reserve power available in a vehicle electrical system;

[0022]FIG. 2 shows a functional circuit diagram of a generator model;

[0023]FIG. 3 shows a functional circuit diagram of a battery model; and

[0024]FIG. 4 shows a simplified equivalent circuit diagram for a vehicle electrical system.

[0025]FIG. 1 shows a schematic circuit diagram of a configuration for ascertaining the power available in a vehicle electrical system, whose central components are a battery model 2 and a generator model 4. The battery and generator models are implemented as software in a data-processing device.

[0026] Battery measured values, particularly the battery voltage or the battery current measured by a battery sensor system 1, are supplied to battery model 2. From these inputs, the state of charge and the state of health of the battery may be ascertained. From this, in turn, it is possible to determine whether a load of the battery, which would result by switching on a specific electrical load, a predefined load limit such as a voltage limit U_(limit) would be undershot. In this context, the voltage limits are set in such a way that the operation of safety-relevant devices is not jeopardized.

[0027] The voltage limits may be modified upon detection of a decline in the battery state of health, e.g., due to battery ageing.

[0028] The battery reserve power ΔP_(battery) may be ascertained from the maximum load current the battery is able to cause to flow until reaching a load limit U_(limit), and from the instantaneous battery internal resistance R_(battery).

[0029]FIG. 3 shows a battery model having battery-state sensing. A voltage limit U_(limit) is predefined for the battery model, from which it ascertains the current I_(load) deliverable until reaching voltage limit U_(limit), as well as the battery internal resistance R_(battery). Applicable for the battery reserve power ΔP_(battery) is:

ΔP _(battery) =I ² _(load) *R _(battery).

[0030] The reserve power ΔP_(generator) available from the generator is ascertained as follows (see FIGS. 1 and 2): First of all, generator model 4 ascertains the instantaneous maximum generator output power P_(generatormax).

[0031] The input quantities of generator model 4 of FIG. 2 are generator voltage U_(generator), generator speed n_(generator) (which is in a fixed ratio to the engine speed) and generator coolant temperature T_(coolant) (which is in a fixed ratio to the generator temperature).

[0032] Generator voltage U_(generator) is calculated on the basis of a voltage drop ΔU_(line) on connection line 3 between the battery and generator, and from the battery voltage. The following applies:

U _(generator) =U _(battery) +ΔU _(line).   (1)

[0033] From this, generator model 4 ascertains instantaneous generator output power P_(generator). For the generator reserve power ΔP_(generator) available from the generator, the following holds true:

ΔP _(generator) =P _(generatormax) −P _(generator).

[0034] The total reserve power available in the system or a power deficit is ascertained (in a processing unit) with the aid of a power balance 5. For the instantaneous total power surplus or power deficit in the vehicle electrical system ΔP_(vehicle electrical system), the following holds true:

ΔP _(vehicle electrical system) =ΔP _(battery) +ΔP _(generator).

[0035] An alternative possibility for ascertaining the generator output power is to determine the generator voltage U_(generator) from the battery voltage U_(battery), the battery current I_(battery) and the electrical load requirements P_(electrical load). A suitable sensor system is necessary to ascertain the battery voltage U_(battery) and battery current I_(battery). Electrical load requirements P_(electrical load) may be determined on the basis of the electrical-load state (on/off) and known electrical-load-requirement parameters. A simplified equivalent circuit diagram of the vehicle electrical system is shown in FIG. 4.

[0036] Generator 10 is connected via a connection line 13 to an electrical load 14 having a resistance R_(v), and via a further line 12 to a battery 11. The following equations may be formulated for ascertaining generator voltage U_(generator):

U _(generator) =I _(generator) *R _(L2) +U _(electrical load),

I _(generator) =I _(battery) +I _(electrical load),

I _(electrical load) =P _(electrical load)/(I _(battery) *R _(L1) +U _(battery)); and

U _(electrical load) =I _(battery) *R _(L1) +U _(battery).

[0037] The generator voltage ascertained in this manner may be used instead of estimation (1) as input quantity for generator model 4 of FIG. 2.

[0038] However, the disadvantage of this method is the relatively high parameterization expenditure for the individual electrical load parameters, which in addition, is a function of the degree to which the vehicle is outfitted. 

What is claimed is:
 1. A method for ascertaining the electric power, provided by a battery (11) and a generator (10), available in an energy supply system, particularly a vehicle electrical system, comprising the following steps: ascertaining a battery reserve power (ΔP_(battery)) using a battery model (2); ascertaining a generator reserve power (ΔP_(generator)) using a generator model (4); and calculating the total available reserve power from the battery reserve power (ΔP_(battery)) and the generator reserve power (ΔP_(generator)).
 2. The method as recited in claim 1, wherein as input quantities, the generator model (4) receives the generator voltage (U_(generator)), the generator speed (n_(generator)) and the generator temperature (T_(generator)) or quantities from which the aforesaid parameters may be derived.
 3. The method as recited in claim 1 or 2, wherein the battery model (2) is adapted to the instantaneous state of the battery with the aid of battery measured values picked up by a battery sensor system (1).
 4. The method as recited in one of the preceding claims, wherein the generator model (4) is static.
 5. The method as recited in one of the preceding claims, wherein the battery model (2) includes a battery-state recognition, with which the state of health of the battery may be assessed.
 6. The method as recited in claim 2, wherein the generator voltage (U_(generator)) supplied to the generator model (4) is estimated up to a predefined degree of utilization of the generator.
 7. The method as recited in claim 6, wherein above the predefined degree of utilization, the generator voltage (U_(generator)) is calculated from the battery voltage (U_(battery)) and the voltage (U_(L2)) dropping on a connection line (13).
 8. The method as recited in one of the preceding claims, wherein the information about the power available in the vehicle electrical system is utilized for an electrical-load management of electrical loads connected in the vehicle electrical system.
 9. The method as recited in one of the preceding claims, wherein limiting values (U_(limit)) are definable for the load of the energy supply system, and particularly for the load of the battery or the generator.
 10. The method as recited in claim 9, wherein measures for reducing energy consumption are initiated if one of the predefined limiting values (U_(limit)) is undershot or threatens to be undershot.
 11. The method as recited in claim 9 or 10, wherein undershooting of one of the limiting values (U_(limit)) is displayed.
 12. The method as recited in one of the preceding claims, wherein it is only possible to switch on an electrical load (14) if there is sufficient reserve power.
 13. The method as recited in one of the preceding claims, wherein power reserves provided by the vehicle electrical system are utilized for a battery thermomanagement.
 14. The method as recited in claim 9 or 10, wherein if one of the limiting values (U_(limit)) is undershot, predefined electrical loads are dimmed or switched off.
 15. A configuration for ascertaining the electric power, provided by a battery and a generator, available in an energy supply system, particularly a vehicle electrical system, comprising a processing unit having: a battery model for ascertaining the reserve power (ΔP_(battery)) available from the battery; and a generator model (4) for ascertaining the reserve power (ΔP_(generator)) available from the generator; the processing unit being able to calculate the total reserve power (ΔP_(vehicle electrical system)) available in the vehicle electrical system from the battery reserve power (ΔP_(battery)) and the generator reserve power (ΔP_(generator)).
 16. The configuration as recited in claim 15, wherein a battery sensor system (1) is provided for ascertaining battery current (I_(battery)) and battery voltage (U_(battery)). 